From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AD21EC35268 for ; Sat, 10 Oct 2020 22:51:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31F832145D for ; Sat, 10 Oct 2020 22:51:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="i63KoTVh" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731135AbgJJWPB (ORCPT ); Sat, 10 Oct 2020 18:15:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730667AbgJJV7Z (ORCPT ); Sat, 10 Oct 2020 17:59:25 -0400 Received: from mail-ot1-x341.google.com (mail-ot1-x341.google.com [IPv6:2607:f8b0:4864:20::341]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 668F1C0613D9 for ; Sat, 10 Oct 2020 14:50:39 -0700 (PDT) Received: by mail-ot1-x341.google.com with SMTP id i12so12347313ota.5 for ; Sat, 10 Oct 2020 14:50:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=zskjUsHTtZxN7/2TQU3peg25br1tT43hRWFs8IXZrR4=; b=i63KoTVhRCCVQE6C47zXN/aote8oxAlq2u8XkZEfRS7C4aCQsGXOTE+Jx6GONLOzLt PE8349J61xYKgijEt/U90UIMaq9DrkU4QY1Tnas9hwBXWmOQCPO26SVsgXlr/ZipK8Ls RMwvBQZd64IkyMtuG55st8dU/i5RoewRXan9Y= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=zskjUsHTtZxN7/2TQU3peg25br1tT43hRWFs8IXZrR4=; b=g2vJ5GZHS8PCi5mF2TT75agHEfwB5gX3/DT4LHYSlmEFwfQNGJUksyWk/WOrn7G90E om7W/y/a77k4F9Hx34Fip68Nhl0fr/xI9LGSrGIc2zHjJ7dFC/dWUcraxrfisUxwYbTl ZZkgjF/5Svr/OFuhh3PDq7FNHkLOZIHdZpmmtKH1xlVdNP1oWHOjLc0FF/zo9qyzlSRZ z8am6KxcE57gxuo9r6gyh9ruLGGBRCZWdusGr9ZFvXl5jO8YqnDT3Tbi6k5tFX26D4lJ McHISxCItOAO45zJ3kpVOALOMd4PLfggsg3Fk/Bzs1L25KFEJUvWaiZ+LLioleMej65s cPpQ== X-Gm-Message-State: AOAM530ui0d+gCHBIq3E4Tm8fydOU484vP4QXVi/FnfwFKjHaMCCLb2k Yp7ZY3GiDxA8+Fn3czMfHAPmtaFDH8SAULi+eU79hn3brd3AKA== X-Google-Smtp-Source: ABdhPJznztyXj83TXT5Po+mKIPpYBLH3P+nInP8snkNIpnPLWv+XbgGvuCQZzJCVdvnd+c/ezVPBdFh+cvOLaSiqshs= X-Received: by 2002:a05:6830:8b:: with SMTP id a11mr2057108oto.303.1602366638562; Sat, 10 Oct 2020 14:50:38 -0700 (PDT) MIME-Version: 1.0 References: <20201009075934.3509076-1-daniel.vetter@ffwll.ch> <20201009075934.3509076-10-daniel.vetter@ffwll.ch> <20201009123421.67a80d72@coco.lan> <20201009122111.GN5177@ziepe.ca> <20201009143723.45609bfb@coco.lan> <20201009124850.GP5177@ziepe.ca> <20201010213554.GD3939@pendragon.ideasonboard.com> In-Reply-To: <20201010213554.GD3939@pendragon.ideasonboard.com> From: Daniel Vetter Date: Sat, 10 Oct 2020 23:50:27 +0200 Message-ID: Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn To: Laurent Pinchart Cc: Tomasz Figa , linux-s390 , linux-samsung-soc , Jan Kara , Kees Cook , KVM list , Linux MM , Mauro Carvalho Chehab , John Hubbard , LKML , DRI Development , Jason Gunthorpe , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Daniel Vetter , Dan Williams , Linus Torvalds , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Sat, Oct 10, 2020 at 11:36 PM Laurent Pinchart wrote: > > Hi Tomasz, > > On Sat, Oct 10, 2020 at 07:22:48PM +0200, Tomasz Figa wrote: > > On Fri, Oct 9, 2020 at 7:52 PM Daniel Vetter wrote: > > > On Fri, Oct 9, 2020 at 2:48 PM Jason Gunthorpe wrote: > > > > On Fri, Oct 09, 2020 at 02:37:23PM +0200, Mauro Carvalho Chehab wrote: > > > > > > > > > I'm not a mm/ expert, but, from what I understood from Daniel's patch > > > > > description is that this is unsafe *only if* __GFP_MOVABLE is used. > > > > > > > > No, it is unconditionally unsafe. The CMA movable mappings are > > > > specific VMAs that will have bad issues here, but there are other > > > > types too. > > > > > > > > The only way to do something at a VMA level is to have a list of OK > > > > VMAs, eg because they were creatd via a special mmap helper from the > > > > media subsystem. > > > > > > > > > Well, no drivers inside the media subsystem uses such flag, although > > > > > they may rely on some infrastructure that could be using it behind > > > > > the bars. > > > > > > > > It doesn't matter, nothing prevents the user from calling media APIs > > > > on mmaps it gets from other subsystems. > > > > > > I think a good first step would be to disable userptr of non struct > > > page backed storage going forward for any new hw support. Even on > > > existing drivers. dma-buf sharing has been around for long enough now > > > that this shouldn't be a problem. Unfortunately right now this doesn't > > > seem to exist, so the entire problem keeps getting perpetuated. > > > > > > > > If this is the case, the proper fix seems to have a GFP_NOT_MOVABLE > > > > > flag that it would be denying the core mm code to set __GFP_MOVABLE. > > > > > > > > We can't tell from the VMA these kinds of details.. > > > > > > > > It has to go the other direction, evey mmap that might be used as a > > > > userptr here has to be found and the VMA specially created to allow > > > > its use. At least that is a kernel only change, but will need people > > > > with the HW to do this work. > > > > > > I think the only reasonable way to keep this working is: > > > - add a struct dma_buf *vma_tryget_dma_buf(struct vm_area_struct *vma); > > > - add dma-buf export support to fbdev and v4l > > > > I assume you mean V4L2 and not the obsolete V4L that is emulated in > > the userspace by libv4l. If so, every video device that uses videobuf2 > > gets DMA-buf export for free and there is nothing needed to enable it. Yeah. And I missed that v4l2 added dma-buf export too. > > We probably still have a few legacy drivers using videobuf (non-2), > > but IMHO those should be safe to put behind some disabled-by-default > > Kconfig symbol or even completely drop, as the legacy framework has > > been deprecated for many years already. > > There's 8 drivers left, and they support a very large number of devices. > I expect unhappy users distros stop shipping them. On the other hand, > videobuf has been deprecated for a loooooooong time, so there has been > plenty of time to convert the remaining drivers to videobuf2. If nobody > can do it, then we'll have to drop support for these devices given the > security issues. Again, the issue here is _only_ with follow_pfn. For videobuf1 this means videbuf-dma-contig.c userptr support is broken. Unlike videobuf2 it means it's broken for all usage (not just zero-copy userptr), because videbuf-dma-contig.c lacks the pin_user_pages path. But that would be easy to add if this poses a problem I think - we just need to carry over the pin_user_pages_fast logic from videbuf2, no driver changes required. But of course I don't think we should do that before someone reports the regression, since videobuf1 userptr is doubly deprecated :-) Everything else keeps working with videobuf1 with my patch series. So depending upon which videobuf1 implementations these 8 drivers use, you might not even have any real breakage there. > We have moved media drivers to staging in the past when there wasn't > enough maintenance effort, we could do so here too. I'm not breaking the world with this, it's really very minimal use-case. At least as far as I'm understanding the entire media subsystem here. -Daniel > > > - roll this out everywhere we still need it. > > > > > > Realistically this just isn't going to happen. And anything else just > > > reimplements half of dma-buf, which is kinda pointless (you need > > > minimally refcounting and some way to get at a promise of a permanent > > > sg list for dma. Plus probably the vmap for kernel cpu access. > > > > > > > > Please let address the issue on this way, instead of broken an > > > > > userspace API that it is there since 1991. > > > > > > > > It has happened before :( It took 4 years for RDMA to undo the uAPI > > > > breakage caused by a security fix for something that was a 15 years > > > > old bug. > > > > > > Yeah we have a bunch of these on the drm side too. Some of them are > > > really just "you have to upgrade userspace", and there's no real fix > > > for the security nightmare without that. > > > > I think we need to phase out such userspace indeed. The Kconfig symbol > > allows enabling the unsafe functionality for anyone who still needs > > it, so I think it's not entirely a breakage. > > -- > Regards, > > Laurent Pinchart -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch